The present invention relates to optical spectrometers and, in particular, to an imaging optical microspectrometer that uses a grism as the dispersive element and is fabricated lithographically.
With the advent of portable, miniature integrated optical systems, there has been an increasing need for microspectrometers that can provide spectral analysis at optical wavelengths. Such microspectrometers have a wide range of potential spectrophotometric applications, including medical diagnostics, wavelength division multiplexing (WDM), and environmental and process analysis.
A particular application of growing importance is for the spectrophotometric analysis of genomic and proteomic microarrays, also termed xe2x80x9cDNA chipsxe2x80x9d or xe2x80x9cmicrochipsxe2x80x9d. These microchips are used extensively to assess the composition of genetic material in a tissue sample for drug discovery research and are likely also to find application in genetic profiling, medical diagnostics and therapy, and the detection of biowarfare and bioterrorism agents. A typical microchip comprises a checkerboard array of perhaps tens of thousands of different DNA molecules, or probes, tethered to a wafer that can be the size of a microscope slide. Genetic material that carries a fluorescent tag, or label, selectively reacts with the DNA molecules on the microchip. The fluorescence from the dye-tagged microchip can then be scanned to provide a color-coded readout of the microarray to determine gene activity.
A planar grating microspectrometer has been developed, primarily for WDM applications. Anderer et al. xe2x80x9cDevelopment of a 10-channel wavelength division multiplexer/demultiplexer fabricated by an X-ray micromachining processxe2x80x9d SPIE 1014, 17 (1988). A later version of this planar grating microspectrometer is marketed by Steag microParts. See xe2x80x9cOptical Devices: Microspectrometers,xe2x80x9d[retrieved on May 9, 2002]. Retrieved from the Internet: less than URL:http://www.microparts.de/english/optics. html greater than . The commercial microspectrometer comprises a monolithic dielectric slab waveguide with an integrated focusing echelette grating formed on the convex edge of the waveguide by a micromolding technique. Light is injected into the waveguide, dispersed by the grating, and focused into ten output optical fibers. The microspectrometer has a spectral range of 380 nm-780 nm and a numerical aperture of about 0.2 with a 50/125 xcexcm optical input fiber. The microspectrometer itself has a footprint of about 29xc3x9714 mm2. Another microspectrometer uses a planar waveguide with a selffocussing phase transmission grating in a compact rectangular design with a footprint of 11xc3x9711 mm2. Sander et al., xe2x80x9cSelffocussing phase transmission grating for an integrated optical microspectrometerxe2x80x9d, Sensors and Actuators A88, 1 (2001).
Neither of these planar microspectrometers is suitable for two-dimensional imaging of a planar object. Also, these planar microspectrometers have a relatively large footprint and cannot easily be fabricated into a microspectrometer array.
The optical microspectrometer of the present invention can spectrally image a line object. A single optical microspectrometer can be used to sequentially scan a planar object, such as a dye-tagged microchip. Because the optical microspectrometer is very compact, multiple optical microspectrometers can be arrayed to provide simultaneous readout of the planar object. The optical microspectrometer can be used to identify dye tags and for coarse WDM. The present invention uses a lithographic process, such as deep X-ray lithography (DXRL), to provide for the monolithic fabrication of the pre-aligned microoptical elements of the optical microspectrometer on a common substrate.
An optical microspectrometer for spectral imaging of light from an object comprises a substrate having a surface with a plurality of microoptical elements monolithically formed thereon and aligned on an optical axis, the microoptical elements comprising a slit through which the light from the object passes, a collimating lens to collimate the light from the slit, a grism to disperse the collimated light from the collimating lens, and an imaging lens to focus the dispersed light from the grism and provide a spectrally resolved image of the slit on a detector. The microoptical elements can further comprise a collecting lens to collect light from the object and a focusing lens to focus the collected light from the collecting lens onto the slit.